#include<iostream>
using namespace std;
#define PI 3.14
int main()
	{
		cout<<"请选择要求的图形（1.圆，2.正方形，3.矩形):"<<endl;
		int type=0;
		int r,s,t,n;
		cin>>type;
		switch(type)
		{
			case 1:
				cout<<"请输入圆的半径："<<endl;
				cin>>r;
				cout<<"圆的面积为："<<r*r*PI<<endl;
				break;
			case 2:
				cout<<"请输入正方形的边长："<<endl;
				cin>>t;
				cout<<"正方形的面积为："<<t*t<<endl;
				break;
			case 3:
				cout<<"请输入矩形的长："<<endl;
				cin>>t;
				cout<<"请输入矩形的宽："<<endl;
				cin>>n;
				cout<<"矩形的面积为："<<t*n<<endl;
				break;
		}
		return 0;
	}
